Induction heating of semisolid billet and control of globular microstructure to prevent coarsening phenomena

An important step in the thixoforming process is the induction heating of the raw materials to the semisolid state. Using this technology, the process behavior is satisfactory from the point of view of reproducibility and temperature control. Therefore, the objectives of this st;dy are to define the correct relationship between coil length and billet length for uniform induction heating and to present the optimal reheating conditions suitable for the thixoforming process (or to secure a fine globular microstructure without liquid segregation). The optimal inductive coil on the induction heating process of semisolid billet machined to 76 mm diameter and 90 mm length to reduce the temperature gradient of the billet and to obtain the globular microstructure was theoretically designed and the suitability of the designed coil dimensions verified by reheating experiments. The globular microstructures of semisolid billet in heating and holding processes were controlled to prevent the coarsening phenomena of Al-7%Si-0.3%Mg alloy and to apply to the thixoforming process. In addition, the effects of the history of processing and induction heating parameters such as reheating time, holding time, holding temperatures, capacity of the induction heating system, and adiabatic material size on the globularization were investigated. It was concluded that in the case of a three-step reheating process, the final holding time is the most important factor and 2 min is suitable to maintain a globular microstructure.